Transport in living plants

This paper provides a general over-view to introduce the subsequent papers on particular topics of plant transport. A revised statement is given of the transport processes reviewed in Ann. Rev. Fluid Mech., 9, 275 (1977), outlining the tissue and cell structures of the plant body which carry out the long distance movements of water, mineral nutrients, and organic material. Some of the questions posed in that review are now better understood, e.g. the breaking of xylem water columns under tension, the loading of sugars into phloem in leaves, and the dissemination of water in leaf veins. Intractable questions remain to which there are no agreed answers, especially the organisation within phloem sieve tubes and the relative roles of the apoplast and symplast in the uptake of water and mineral ions by roots. New techniques are available for tracing water-soluble substances at high resolution in microscopic preparations which may lead to the resolving of some of these questions.